Stable austenitic stainless steel for hydrogen storage vessels

ABSTRACT

An austenitic stainless steel composition is provided that is resistant to embrittlement due to hydrogen and/or low temperature. The steel composition comprises chromium (Cr) at greater than or equal to about 17% by weight; nickel (Ni) at less than or equal to about 13% by weight; nitrogen (N) at greater than 0.16% by weight. The steel is substantially free of molybdenum (Mo). In various embodiments, the steel is used to form a surface of a hydrogen storage vessel that contacts hydrogen and is resistant to hydrogen and low temperature (less than or equal to about −100° C.) embrittlement. Methods of storing hydrogen in vessels made of the hydrogen embrittlement resistant austenitic steel composition are also provided.

FIELD

The present invention relates to corrosion resistant stainless steel,and more particularly to a stable austenitic stainless steel for vesselsthat store pressurized hydrogen.

BACKGROUND

Fuel cells have been proposed as a power source for automotive vehiclesand other applications. Fuel cell systems include a fuel cell stack thatproduces electrical energy based on a reaction between ahydrogen-containing feed gas and an oxidant feed gas (e.g., oxygen oroxygen-containing air).

Hydrogen storage is a technology critical to fuel cell operation andother kinds of power generating applications. Typical power generatingsystems include a storage vessel that stores and supplies ahydrogen-containing feed stream to a power plant (e.g., the fuel cellstack) that consumes hydrogen. The hydrogen-containing feed stream canbe stored within the storage vessel as a liquid or a compressed gas. Incertain applications, the hydrogen-containing feed gas is preferablystored at a temperature of as low as approximately −250° C. to −260° C.as a liquid or alternatively within a temperature range of approximately−100° C. to 100° C. as a pressurized gas.

The handling and containment of hydrogen-containing streams can posedifficulties. Many materials (e.g., high strength ferritic steels) havethe potential to be susceptible to hydrogen corrosion, i.e., hydrogenembrittlement. Hydrogen embrittlement is a form of brittle cracking thatcan occur in various steels and alloys when the materials are exposed tohydrogen.

Further, low temperatures can potentially contribute a brittle fracturebehavior of ferritic steels, irrespective of atmospheric conditions. Forlow temperature applications, such as those where the temperaturereaches −100° C. or less, austenitic steels are the most ductile steel.Most austenitic stainless steels have a metastable austenitic structure,meaning the austenitic structure is only stable down to a characteristictemperature, referred to as the “M_(s)” temperature. When the materialis cooled and the increase in free enthalpy exceeds ΔG, parts of theaustenitic body face centered structure transform into cubic bodycentered martensite. The value of ΔG is generally believed to bestrongly dependent on the chemical composition of the steel. Theformation of martensite contributes to embrittlement of the material,either due to low temperature, exposure to hydrogen, or both. Thus, itis optimal to minimize the formation of martensite. Usually thestability of the austenite is enhanced by increasing the nickel (Ni)content of the steel.

Higher grade materials have generally been used to avoid potentialfailure of hydrogen storage and handling equipment. For example, highergrades of austenitic stainless steels having relatively high amounts ofnickel, chromium, manganese, and/or molybdenum suffer less from hydrogenembrittlement and/or low temperature embrittlement. However, thesematerials are quite costly, and there is a need for low cost, durablematerials for hydrogen storage and handling.

SUMMARY

In various embodiments, the present invention provides a hydrogenstorage vessel comprising a surface that comprises an austeniticstainless steel composition comprising chromium (Cr) at greater than orequal to about 17% by weight; nickel (Ni) at less than or equal to about13% by weight; and nitrogen (N) at greater than 0.16% by weight. Thesteel composition is preferably substantially free of molybdenum (Mo).Further, the surface is in contact with hydrogen and is preferablyresistant to embrittlement to a temperature of about −100° C.

In certain embodiments, the invention provides an austenitic steelcomposition that is resistant to hydrogen embrittlement. The compositioncomprises carbon (C) at less than or equal to about 0.07% by weight;nickel (Ni) at less than or equal to about 10.5% by weight; chromium(Cr) at greater than or equal to about 17% by weight; and nitrogen (N)at greater than 0.18% by weight. The composition is preferablysubstantially free of molybdenum (Mo).

In other embodiments, the invention provides a method for storinghydrogen comprising providing a storage vessel resistant toembrittlement to a temperature of at least about −100° C. The vessel hasa surface comprising an austenitic stainless steel compositioncomprising chromium (Cr) at greater than or equal to about 17% byweight; nickel (Ni) at less than or equal to about 13% by weight; andnitrogen (N) at greater than 0.16% by weight. The composition ispreferably substantially molybdenum (Mo) free. The method furthercomprises transferring a hydrogen-containing stream to the vesselwherein the stream is in contact with the surface. Thehydrogen-containing stream is stored in the vessel, where the surfacedoes not experience embrittlement. The hydrogen-containing stream isthen stored in the vessel without any embrittlement or associateddetrimental effects or damage caused by it.

Further areas of applicability of the present invention will becomeapparent from the detailed description provided hereinafter. It shouldbe understood that the detailed description and specific examples, whileindicating the preferred embodiment of the invention, are intended forpurposes of illustration only and are not intended to limit the scope ofthe invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic illustration of an exemplary fuel cell systemincluding a hydrogen storage vessel according to the present invention;

FIG. 2 is a schematic illustration of a hydrogen storage vesselaccording to an embodiment of the present invention; and

FIG. 3 is a schematic illustration of a hydrogen storage vesselaccording to an alternate embodiment of the present invention.

DETAILED DESCRIPTION

The following description of the preferred embodiments is merelyexemplary in nature and is in no way intended to limit the invention,its application, or uses. “A” and “an” as used herein indicate “at leastone” of the items is present; a plurality of such items may be present,when possible. All percentages indicated are on a weight basis, unlessexpressly indicated as otherwise.

Generally, stainless steels are divided into three classes based uponthe predominant phase constituent of the microstructure, namely:martensitic, ferritic or austenitic. When nickel and chromium are addedto steel in sufficient amounts, the crystal structure changes toaustenite. Higher nickel content in a stainless steel improves theresistance to hydrogen embrittlement and maintains an austeniticstructure, while lower nickel content potentially leads to a metastablestructure where the austenite can transform into martensite when exposedto low temperatures. Austenitic stainless steels are steel alloystypically having a centered cubic-lattice structure. Preserving thestability of the austenitic structure is important for obtaining goodresistance against embrittlement due to exposure to hydrogen, lowtemperatures, or both.

Thus, the hydrogen storage vessels of the various embodiments of theinvention preferably comprise at least one surface constructed fromaustenitic stainless steel compositions. Further, as described above, itis preferable that the surface comprising an austenitic structuremaintains good resistance against embrittlement. As used herein,“embrittlement” refers to a form of brittle fracture or cracking thatoccurs in a material when exposed to certain environmental conditions,such as hydrogen and/or low temperatures. Hydrogen embrittlement inparticular refers to the deterioration of material properties(especially crack growth rate) due to the influence of hydrogen. Inaccordance with various embodiments, it is preferred that the steelmaterials of the invention are resistant to embrittlement at lowtemperatures. Thus, temperatures at which embrittlement does not occurfor compositions of the invention are about 0° C. in some embodiments;about −50° C.; about −100° C.; about −200° C.; and optionally about−250° C. in certain embodiments, depending on the application, as willbe described in more detail below. In some applications, the steelmaterials preferably withstand embrittlement at temperatures as low asabout −260° C.

A typical austenitic steel composition has chromium at greater than orequal to about 16% and nickel at greater than or equal to about 8%.Austenitic stainless steels include the 300 series in stainless steelgrades. As appreciated by those of skill in the art, varying amounts ofelements, such as nickel, chromium, molybdenum, and manganese, can beadded and the greater the amounts of these elements that are included,the higher the grade of steel. Of the commercially available austeniticsteel compositions, only higher grades (with more expensive alloyingelements) are recognized to withstand hydrogen embrittlement.

One exemplary lower grade steel is 316L where carbon (C) is present atless than or equal to 0.03%, chromium (Cr) at about 17%, nickel (Ni) atabout 9%, manganese (Mn) at about 2%, and molybdenum (Mo) at about 2.5%.“L” designates low carbon content. 316L is substantially free ofnitrogen. It is known that this grade suffers from hydrogenembrittlement at various conditions. A higher grade austenitic stainlesssteel is Grade 317LMN that has carbon (C) at less than or equal to0.03%, chromium (Cr) from between about 16.5-18.5%, nickel (Ni) fromabout 13.5-17.5%, manganese (Mn) from about 1-2%, and molybdenum (Mo)from about 4-5%. In the 317LMN grade, the “M” and “N” designationsindicate that the composition contains increased levels of molybdenumand nitrogen respectively. The 317LMN is generally regarded as a stableaustenitic steel, which means that the structure remains austeniticregardless of typical industrial temperature conditions.

The degree of embrittlement depends greatly on the strength andcomposition of the steel. As previously discussed, the addition ofchromium, nickel, manganese, and molybdenum to stainless steelcompositions is desirable; however, it is also costly. Therefore,traditional stainless steels present a trade-off between cost andresistance to embrittlement and/or good performance through a range oftemperatures. Thus, in accordance with preferred embodiments of thepresent invention, low grade austenitic stainless steel compositions aremodified to improve embrittlement resistance. As used herein, “modified”means that a traditional relatively low grade steel composition hasincreased nitrogen content while having lower amounts of expensivealloying elements, in accordance with the principles of the presentinvention. The performance in terms of hydrogen embrittlement of theinventive compositions is comparable to higher grade austeniticstainless steels.

Hence, various embodiments of the invention provide an inexpensive,modified lower grade austenitic stainless steel composition that can beused in hydrogen storage applications. Such compositions have increasednitrogen content, which provides a relatively low cost, high performanceembrittlement resistant stainless steel. In this manner, less expensivesteels (i.e., steels having lower nickel, chromium, and molybdenumcontent) can be employed, while still having high resistance to hydrogenembrittlement, as well as sufficient toughness (that counteractsembrittlement) at low temperatures.

The increase in nitrogen content, without increasing nickel content,improves the stability of the austenitic structure and resistance tohydrogen embrittlement and/or low temperature. In various embodiments,the nickel content is limited in the compositions of the presentinvention because of its high cost, as well as the fact that itspresence decreases the solubility of nitrogen in the smelting process.Further, in various embodiments, the steel compositions aresubstantially free of molybdenum. The phrase “substantially free” meansthat the content of molybdenum is not detectable above an impurity levelin the steel composition. As such, the austenitic stainless steelcompositions of the present invention have enhanced resistance toembrittlement and increased toughness at lower temperatures withoutincreased cost.

In accordance with various embodiments of the invention, a lower gradeinexpensive austenitic stainless steel is thus modified. The most commonaustenitic steels are the relatively less expensive lower 304 grades,which typically contain about 17-20% chromium, and about 8% nickel. The304 grades are substantially free of molybdenum. By way of example, anexemplary low Grade 304 austenitic stainless steel has carbon (C) atless than or equal to 0.08%, chromium (Cr) from between about 17-19.5%,nickel (Ni) from about 8-10.5%, manganese (Mn) at less than or equal toabout 2%, where the composition has no molybdenum (Mo) added, i.e., thesteel is substantially free of Mo. These grades are typical metastablesteels meaning that the alloying content of nickel is not generallyviewed to be high enough to preserve an austenitic structure at lowtemperatures.

In the following Table 1, various compositions illustrate the chemicalcomposition of a Standard AISI Grade 317LMN steel (a higher gradeaustenitic steel), a Standard AISI Grade 304 steel (a lower gradeaustenitic steel), a Standard AISI Grade 304N (a commercially availablelower grade steel with relatively low levels of nitrogen) and twoaustenitic examples prepared in accordance with the present invention,namely Examples 1 and 2, of two different embodiments of modified Grade304 steels. The amounts of each element in the steel are expressed aspercentages by weight.

TABLE 1 M_(s) Steel C Si Mn P S Cr Mo Ni N T (° C.) (*) Grd. ≦0.03 ≦0.751-2 ≦0.045 ≦0.03 17-20   4-5 13.5-17.5   0.1-0.2  −305 317LMN Std. Grd.304 ≦0.07 ≦1 ≦2 ≦0.045 ≦0.03 17-19.5 0 8-10.5 <0.11 +148 Std. Grd. 304 N≦0.08 ≦1 ≦2 ≦0.045 ≦0.03 18-20   0 8-10.5 0.1-0.16 −60 Std. Example 10.02-0.07 ≦1 1-2 ≦0.045 ≦0.03 18-19.5 0 8-10.5 >0.22 −253 Example 2≦0.07 ≦1 ≦2 ≦0.045 ≦0.03 17-19.5 0 8-10.5 >0.18 −151 (*) Calculatedvalue

As discussed above, the M_(s) temperature is the temperature at which amartensitic transformation starts, i.e., the austenitic structuretransforms to a martensitic structure. In Table 1, the predicted M_(s)temperature is obtained by calculating the M_(s) temperature fromEquations 1-3 set forth below and using the maximum predicted value fromthe three equations. In Equations 1-3, “a” is weight % of carbon in thesteel composition; “b” is weight % of nickel; “c” is weight % ofsilicon; “d” is weight % of manganese; “e” is weight % of chromium; “f”is weight % of nickel; “g” is weight % of copper; and “h” is weight % ofmolybdenum. The equations are as follows:

M _(s)(° C.)=1305−1665(a+b)−28(c)−33(d)−42(e)−61(f)  (Eqn. 1)

M _(s)(° C.)=1182−1456(a+b)−37(e)−57(f)  (Eqn. 2)

M _(s)(° C.)=502−810(a)−1230(b)−13(d)−30(f)−12(e)−54(g)−46(h)  (Eqn. 3)

Equation 1 is provided in Eichelmann, et al., “The Effect of Compositionon the Temperature of Spontaneous Transformation of Austenite toMartensite in 18-8-type Stainless Steels,” 45 Transactions of theA.S.M., page 95 (1953). Equation 2 is provided in Monkman, et al.,“Computation of M_(s) for Stainless Steels,” Metal Progress, page 95(April 1957). Equation 3 is provided in Pickering, “Physical Metallurgyand the Design of Steels,” Appl. Sci. Pub. Ltd., London, (1978).

Thus, the predicted M_(s) temperatures indicate whether a steel willwithstand embrittlement at certain temperatures. As described above,stability is strongly dependent on the chemical composition of thesteel. It is believed that increasing the Ni content appears to cause agreat reduction in M_(s) temperature. However, in accordance withvarious embodiments of the invention, an increased nitrogen (N) canprovide desirable M_(s) temperatures without needing to increase nickelcontent or similar expensive elements. In accordance with variousembodiments of the invention and as described previously above, it ispreferred that the steel compositions are in the austenite phase andthat the steel is used in an environment above the M_(s) temperature topreserve the austenite microstructure in the steel.

In accordance with certain embodiments of the invention illustrated byExample 1, the modified Grade 304 steel having a nitrogen content ofgreater than about 0.22% is particularly well-suited for storing liquidhydrogen-containing fluids. Liquid hydrogen is typically stored attemperatures below −200° C., and in some cases temperatures that are aslow as approximately −250° C. to −260° C. At temperatures at, near, orin certain embodiments below −250° C., the steel of Example 1 willretain its austenitic structure, toughness properties, and resistance toembrittlement, especially in the presence of hydrogen.

In certain embodiments, the Grade 304 modified steel of Example 2 of theinvention is useful for compressed gas hydrogen storage applications andincludes a nitrogen content of greater than about 0.18%. Gaseous (andpressurized) hydrogen is typically stored within a temperature range ofapproximately −100° C. to about 100° C.; thus, Example 2 preferablyretains its austenitic structure, toughness properties, and resistanceto hydrogen embrittlement at least within the range of about −100° C. toabout 100° C.

The 317LMN grade has higher molybdenum, nickel, and chromium contentthat makes it significantly more expensive than the 304 grade steel. Theincreased amounts of molybdenum, nickel, and chromium enhanceembrittlement resistance. Both the modified Grade 304 steels of Examples1 and 2, according to the present invention, are significantly lessexpensive than grade 317LMN steel, but are suitable for use in hydrogenstorage vessels.

In various embodiments, the present invention provides a hydrogenstorage vessel comprising an austenitic stainless steel composition thatcomprises chromium (Cr) at greater than or equal to about 17% by weight;nickel (Ni) at less than or equal to about 13% by weight; and nitrogen(N) at greater than 0.16% by weight, preferably having nitrogen atgreater than about 0.18% by weight, and in some embodiments havingnitrogen greater than about 0.22% by weight. In certain embodiments, thenickel is less than or equal to about 12%, more preferably less than12%, even more preferably less than 11%, and in some embodiments, lessthan about 10.5%. The steel composition is substantially free ofmolybdenum (Mo), and is resistant to embrittlement. Preferably thecomposition has a stable austenitic structure down to temperatures ofabout −250° C., the temperature of liquid hydrogen. Preferably at leastone surface of the vessel is constructed of such a composition. Thesurface contacts the hydrogen.

In some embodiments, the nitrogen is greater than about 0.18% by weight;optionally greater than about 0.22% by weight. The composition issubstantially free of molybdenum (Mo). In some embodiments, the steelcomposition is resistant to hydrogen embrittlement and consistsessentially of: less than or equal to about 0.07% by weight of carbon(C); less than or equal to about 1.0% by weight of silicon (Si); lessthan or equal to about 2.0% by weight of manganese (Mn); less than orequal to about 0.045% by weight of phosphorous (P); less than or equalto about 0.03% by weight sulfur (S); less than or equal to about 13% byweight nickel (Ni); greater than or equal to about 17% by weightchromium (Cr); greater than 0.16% by weight of nitrogen (N), and thebalance iron (Fe) and incidental impurities. In certain embodiments, thenickel is less than or equal to about 12%, more preferably less than12%, even more preferably less than 11%, and in some embodiments, lessthan about 10.5%. The composition is resistant to hydrogen embrittlementand preferably has a stable austenitic structure down to about −150° C.The composition is durable, strong, and resistant to hydrogenembrittlement to a typical temperature of gaseous hydrogen forautomotive applications.

The steel compositions of the present invention can be used to makehydrogen storage vessels that have operational safety via increasedstructural stability and capability to withstand potential embrittlementfrom exposure to the hydrogen-containing fluids. Because of theincreased structural stability, the storage vessel can have a thinnerwall thickness providing decreased weight and size over storage vesselsmade from traditional higher grade austenitic stainless steel.

FIG. 1 shows an exemplary fuel cell system 10. The fuel cell system 10includes a fuel cell stack 12, a hydrogen storage vessel 14 and acompressor 16. In various embodiments, the fuel cell system is in avehicular or mobile power plant. The fuel cell system 10 furtherincludes a pressure maintaining system 18 and a pressure managementsystem 19. The pressure maintaining system 18 regulates the pressurewithin the hydrogen storage vessel 14 and operates independent of thefuel cell stack 12 (i.e., regardless of whether the fuel cell stack isON or OFF). The pressure management system 19 regulates the pressure ofthe hydrogen provided to the fuel cell stack 12 and operates when thefuel cell stack 12 is ON.

The compressor 16 provides pressurized, oxygen-rich air to a cathodeside of the fuel cell stack 12 through a regulator 20. Reactions betweenthe hydrogen and oxygen within the fuel cell stack 12 generateelectrical energy that is used to drive a load (not shown). It should benoted that hydrogen provided to the fuel cell stack 12 preferably has ahigh purity with a minimum amount of undesirable contaminants, such ascarbon monoxide. Thus, the hydrogen provided to a fuel cell stack 12tends to have a relatively high concentration of hydrogen. A controlmodule 22 regulates overall operation of the fuel cell system based onload input and operating parameters of the fuel cell system. The loadinput indicates the desired electrical energy output from the fuel cellstack 12. For example, in the case of a vehicle, the load input couldinclude a throttle.

FIG. 2 shows an embodiment of the present invention, where the hydrogenstorage vessel 14 is in the exemplary form of a tank 30. A passage 32 isprovided for permitting ingress and egress of a hydrogen-containingfluid (i.e., liquid or gas). The tank 30 has an interior compartment 34for storage of the hydrogen-containing fluid. In various embodiments ofthe present invention, the hydrogen storage vessel 14 can contain ahighly pressurized fluid, thus the hydrogen storage vessels, such astank 30 are preferably designed to be a high pressure storage tank. By“high pressure” it is meant that the hydrogen-containing fluid is storedat pressures up to or exceeding about 70 MPa. In various embodiments,the hydrogen-containing fluid is a pressurized gas. In otherembodiments, the hydrogen-containing fluid stream is a liquid. Asdescribed above, the gas is preferably stored at a temperature range ofabout −100° C. to about 100° C. A hydrogen-containing liquid ispreferably stored at temperatures as low as −250° C. As was previouslydescribed above, the austenitic steel compositions of the presentinvention having greater than or equal to about 0.18% nitrogen aredurable and resistant to hydrogen-embrittlement through the range oftemperatures of about −100° C. to about 100° C. Thus, surfaces of thetank 30 that contact the hydrogen-containing fluid stream preferably areconstructed of steel materials of the invention that have gooddurability through these temperature ranges. Likewise, when surfaces ofthe tank 30 contact hydrogen-containing liquid, the austenitic steelcomposition preferably can withstand temperatures down to about −250° C.Thus, it is preferred that the steel composition comprises greater thanor equal to about 0.22% nitrogen.

Walls 36 of the tank structure form the interior compartment 34 andexterior structure 38 of the tank 30. The portion of the interiorcompartment 34 that directly contacts the hydrogen-containing stream ispreferably fabricated of the modified hydrogen embrittlement resistantaustenitic steel of the present invention. As appreciated by one ofskill in the art, the designs shown for the hydrogen storage vessels aresimplified, and the storage vessel may be in various different forms orshapes, and may include various additional equipment and passages.

In another embodiment, the hydrogen storage vessel is in the form of analternate configuration of an exemplary and simplified tank 40, as shownin FIG. 3. The tank has an inner liner 42 that forms a continuoussurface of an interior storage compartment 44 that contacts and containsthe hydrogen-containing fluid. The liner 42 is disposed within theexterior walls 46 of tank 40. A passage 48 for transportinghydrogen-containing streams to and from the interior storage compartment44 is provided. In the present embodiment, the austenitic steelcomposition of the present invention forms the liner 42. However, theexterior walls 46 of tank 40 may be fabricated from other less expensivematerials. The material that contacts and contains thehydrogen-containing stream is durable and resistant to hydrogenembrittlement; however the remainder of the tank 40 structure can befabricated from other materials to realize a cost savings, an increasein strength and durability, and/or weight reduction. Further, in certainembodiments, an insulator material 50 can be provided in an intermediateregion between the liner 42 and the exterior walls 46 to maintain thedesired storage temperatures for the hydrogen fluid.

In various embodiments, a method is provided for storing and/orcontaining hydrogen. The method comprises providing a storage vesselhaving a surface that is resistant to embrittlement to a temperature ofat least about −100° C. As appreciated by one of skill in the art, thesurface of the vessel that is resistant to hydrogen embrittlement cancomprise any of the various embodiments of austenitic stainless steelcompositions according to the present invention, as described above. Inone embodiment, the vessel has a surface comprising an austeniticstainless steel composition comprising chromium (Cr) at greater than orequal to about 17% by weight; nickel (Ni) at less than or equal to about13% by weight; and nitrogen (N) at greater than 0.16% by weight. Thecomposition is preferably substantially molybdenum (Mo) free.

The method further comprises transferring a hydrogen-containing streamto the vessel wherein the stream is in contact with the surface. Incertain embodiments, the stream is pressurized prior to or during thetransferring. The hydrogen-containing stream is stored in the vessel andthe surface(s) of the vessel that contact the stream do not experienceembrittlement. The hydrogen-containing stream is then stored in thevessel without any embrittlement or associated detrimental effects ordamage caused by it.

Steels are typically made in furnaces, such as basic oxygen processfurnaces (BOF), open hearth furnaces (OHF), and electric arc furnaces(EAF). Most steel is now made in integrated steel plants using a versionof the BOF process or in specialty steel plants that use EAF process. Inan exemplary BOF process, hot liquid blast furnace metal, scrap, andfluxes are charged to a converter (furnace). Nitrogen and other alloyingelements are added at the desired concentrations. Nitrogen can beintroduced into the steel composition by charging the furnace withchromium nitride (CrN), manganese nitride (MnN), or mixtures thereof,for example. A lance is lowered into the converter and high-pressureoxygen is injected. The oxygen combines with and removes the impuritiesin the charge. These impurities consist of carbon as gaseous carbonmonoxide, and silicon, manganese, phosphorus and some iron as liquidoxides, which combine with lime and/or dolomite to form the steel slag.At the end of the refining operation, the liquid steel is poured into aladle while the steel slag is retained in the vessel and subsequentlytapped into a separate slag pot. In this manner, steel compositions ofthe invention can be made to have the desired elemental content,including the desired nitrogen content.

The description of the invention is merely exemplary in nature and,thus, variations that do not depart from the gist of the invention areintended to be within the scope of the invention. Such variations arenot to be regarded as a departure from the spirit and scope of theinvention.

1. A hydrogen storage vessel comprising a surface that comprises anaustenitic stainless steel composition comprising: chromium (Cr) atgreater than or equal to about 17% by weight; nickel (Ni) at less thanor equal to about 13% by weight; and nitrogen (N) at greater than 0.16%by weight, wherein the steel composition is substantially free ofmolybdenum (Mo), and wherein the surface is in contact with hydrogen andis resistant to embrittlement to a temperature of about −100° C.
 2. Thevessel of claim 1, wherein the composition comprises nitrogen (N) atgreater than or equal to about 0.18% by weight.
 3. The vessel of claim2, wherein the composition comprises nickel (Ni) at less than or equalto about 10.5% by weight.
 4. The vessel of claim 1, wherein thecomposition comprises nitrogen (N) at greater than or equal to about0.22% by weight.
 5. The vessel of claim 4, wherein the composition isresistant to embrittlement to a temperature of about −250° C.
 6. Thevessel of claim 1, wherein the composition is resistant to hydrogenembrittlement at temperatures in the range of about −100° C. to about100° C.
 7. The vessel of claim 1, wherein the vessel is charged with apressurized hydrogen-containing gas, and the surface is in contact withsaid pressurized hydrogen-containing gas.
 8. The vessel of claim 1,wherein the vessel is a high pressure storage tank.
 9. The vessel ofclaim 1, wherein the surface forms a liner that contains the hydrogen.10. A vehicular power plant comprising the vessel of claim 1, whereinthe hydrogen storage vessel stores hydrogen that is provided as a fuelto the vehicular power plant.
 11. An austenitic steel composition thatis resistant to hydrogen-embrittlement comprising: carbon (C) at lessthan or equal to about 0.07% by weight; nickel (Ni) at less than orequal to about 10.5% by weight; chromium (Cr) at greater than or equalto about 17% by weight; nitrogen (N) at greater than 0.18% by weight;and wherein said composition is substantially free of molybdenum (Mo).12. The composition of claim 11, wherein the composition furthercomprises silicon (Si) at less than or equal to about 1.0% by weight;manganese (Mn) at less than or equal to about 2.0% by weight; phosphorus(P) at less than or equal to about 0.045% by weight; sulfur (S) at lessthan or equal to about 0.03% by weight; and the balance iron (Fe) andincidental impurities.
 13. The composition of claim 11 wherein saidcomposition comprises nitrogen (N) at greater than or equal to about0.22% by weight.
 14. A method for storing hydrogen comprising: a.providing a storage vessel resistant to embrittlement to a temperatureof at least about −100° C., said vessel having a surface comprising anaustenitic stainless steel composition comprising chromium (Cr) atgreater than or equal to about 17% by weight; nickel (Ni) at less thanor equal to about 13% by weight; and nitrogen (N) at greater than 0.16%by weight; wherein said composition is substantially molybdenum (Mo)free; b. transferring a hydrogen-containing stream to the vessel whereinsaid stream is in contact with the surface; and c. storing saidhydrogen-containing stream in said vessel, wherein the surface does notexperience embrittlement.
 15. The method of claim 14, wherein saidaustenitic stainless steel composition comprises nitrogen (N) at greaterthan about 0.18%.
 16. The method of claim 14, wherein said austeniticstainless steel composition comprises nitrogen at greater than about0.22% by weight.
 17. The method of claim 14, wherein said vessel isresistant to embrittlement to a temperature of at least about −250° C.